Automatic missile guidance system

ABSTRACT

The automatic missile guidance system comprises a sight with which a gunner establishes a line-of-sight from the gun position to the target. When the missile is launched, a source of pulsating, radiant energy on the rear of the missile is detected by a guidance unit at the sight. The guidance unit produces steering commands related to the deviation of the missile from the line-of-sight. Means interconnecting the guidance unit and the missile transmits the guidance signals to the missile to direct it along the line-of-sight. This guidance unit to missile connection may be wires which unreel from the missile as it proceeds towards its target.

United States Patent [151 Barhydt'et al. 1 Jan. 16, 1973 [54] AUTOMATICMISSILE GUIDANCE SYSTEM [57] ABSTRACT Inventors: nflfnilmn y 3211Billowvista The automatic missile guidance system comprises 11 Drive,Playa del y Callf- 90291; sight with which a gunner establishes aline-of-sight Spencer Howe, Stewart from the gun position to the target.When the missile Avenue Los Angeles, Cahf' 90045 is launched, a sourceof pulsating, radiant energy on 22] Fil d; 22, 1969 the rear of themissile is detected by a guidance unit at the sight. The guidance unitproduces steering com- [211 Appl' 870377 mands related to the deviationof the missile from the line-of-sight. Means interconnecting theguidance unit [52] U.S. Cl "2445.12, 244/3.16 and the missile transmitsthe guidance signals to the g F4 g missile to direct it along theline-of-sight. This [58] Field of Search v.244/3.l2, 3.16

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thomas H. WebbAtt0rneyJames K. Haskell and Allen A. Dickes, Jr.

guidance unit to missile connection may be wires which unreel from themissile as it proceeds towards its target.

23 Claims, 12 Drawing Figures PATENTEDJAI 16 1913 SHEET 2 OF 6 HamiltonBorhydf, George T. Hahn,

Spencer D. Howe,

NVENTORS.

Allen A. Dicke,dr.,

PATENTED JAN 16 I973 SHEET 3 or 5 Hamilton Borhydf, Geor T. Hahn, S D.How

ge pencer INVEN TOPS.

Allen A.Dicke, Jr.,

AGE/VT.

PATENTED JM 1 6 I975 SHEET U [1F 6 IOO- O O .822 02 :30 3a rees AngularDistance From Center Of Reficle In Deg 6 rfi d 8 Mmw 0 6 OHH k B S C n mD G N m mw A mmeN B EP m HGS H A Time (seconds) AGE/VT.

AUTOMATIC MISSILE GUIDANCE SYSTEM CROSS REFERENCE This application is asubstitute for US. Pat. application, Ser. No. 107,861, filed May 4,1961, for AUTO- MATIC MISSILE GUIDANCE SYSTEM, Hamilton Barhydt, GeorgeT. Hahn and Spencer D. Howe, Inventors.

BACKGROUND The present invention relates to apparatus for remotelycontrolling the flight of self-propelled rockets and, more'particularly,to a guidance system for automatically providing guidance signals to amissile, enabling it to follow a line-of-sight path to a target.

Guidance of small, self-propelled missiles by manual operation ofcontrols that generate guidance signals is difficult, due to therelatively slow reflexes of human operators. An additional disadvantageof manual guidance is the necessity that the operator be highly skilledor highly trained.

In automatic guidance of a missile, it is desirable that the equipmentfor tracking the target and providing guidance signals remain at thelaunching point, rather than be incorporated into the missile. By havingthe tracking and guidance equipment at the launching point, the missileis lighter in weight and, therefore, easier to handle. Furthermore, themissile is less likely to malfunction, because it is less complex andthe missile is also less expensive.

When the target tracking and missile guidance equipment is to beportable, it must be small, light and compact. On the other hand, itmust operate efficiently, in spite of close proximity to the ground.Radar tracking equipment, for example, is subject to reflection fromirregularities in the terrain, usually known as ground clutter. Infraredtracking equipment is subject to unwanted radiation from background andsurrounding objects, as well as from the sun, if it is in the field ofview;

SUMMARY The automatic missile guidance system comprises a sight withwhich a gunner establishes a line-of-sight from the gun position to thetarget. When the missile is launched, a source of pulsating, radiantenergy on the rear of the missile is detected by the sight. A guidanceunit connected to the sight produces steering commands related to thedeviation of the missile from the line-of-sight. Means interconnectingthe guidance unit and the missile transmit the guidance signals to themissile.

Accordingly, it is an object of the present invention to provide anautomatic missile guidance system that is small in size, light in weightand relatively inexpensive. Another object of the invention istheprovision of a missile guidance system that is automatic in nature anddoes not require guidance signals to be manually generated by a humanoperator. Yet another object of the present invention is to provide anautomatic missile guidance system that includes missile trackingequipment of a simple, yet effective type. A further object of theinvention is the provision of a missile guidance system that includesinfrared tracking equipment that is relatively insensitive to backgroundradiation from the sun and other intense sources of radiation.

The following specification and the accompanying drawings respectivelydescribe and illustrate an exemplification of the present invention.Consideration of the specification and the drawings will provide acomplete understanding of the invention, including the novel featuresand objects thereof. Like reference characters are used to designatelike parts throughout the figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial representationof an embodiment of an automatic missile guidance system, in accordancewith the present invention;

FIG. 2 is a functional block diagram of the missile guidance system ofFIG. 1;

FIG. 3 is a side view of a missile suitable for use in the missileguidance system of FIGS. 1 and 2;

FIG. 4 is a rear view of the missile of FIG. 3;

FIG. 5 is a side view, partly in section, of an embodiment of aninterrupted infrared radiation source, in accordance with the invention,for use in the missile guidance system of FIGS. 1 and 2;

FIG. 6 is an end view of the interrupted radiation source of FIG. 5;

FIG. 7 is a side view, partly in section, of an embodiment of aninfrared telescope, in accordance with the invention, for use in themissile guidance system of FIGS. 1 and 2;

FIG. 8 is a reduced transverse sectional view of the infrared telescopetaken substantially as indicated by line 88, FIG. 7, and illustratingthe reference signal generators associated with the reticle;

FIG. 9 is an enlarged view of a reticle modulation pattern for use inthe infrared telescope of FIG. 7;

FIG. 10 is a graph illustrating the modulation characteristic of thereticle pattern of FIG. 9;

FIG. 11 is a circuit diagram in block form of a signal processingcircuit, in accordance with the present invention and used in themissile guidance system of FIGS. 1 and 2; and

FIG. 12 is a graph illustrating the gain characteristic of the variablegain amplifier in the signal processing circuit of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with these andother objects of the invention, a guidance unit is provided that may besimilar in size and appearance to a rifle. The guidance unit is providedwith a visual sight, or telescope, through which an operator views thetarget, thus establishing a line-ofsight between the launching point andthe target. A remotely-controlled missile launched toward the target isviewed by an infrared telescope disposed on the guidance unit andaligned with the visual telescope. The missile is provided with aperiodically interrupted infrared source that emits a distinctivefrequency, pulsating radiation that is intercepted by the infraredtelescope, enabling subsequent circuits to discriminate againstbackground radiation. A rotating reticle is provided in the infraredtelescope to amplitude modulate the intercepted pulsating radiant energyto provide information as to the magnitude and direction of deviationsof the missile from the line-of-sight. The infrared telescope isprovided with dual infrared detection cells to convert the modulatedradiant energy into a modulated carrier wave that is supplied to asignal processing circuit. The use of two detection cells permits theinfrared telescope to selectively have both a wide field of view and anarrow field of view, the latter having greater sensitivity. Thedetection cell for the large field of view is not saturated by radiationfrom intense sources of background energy in its field of view.Provisions are made for automatically switching from the wide field cellto the narrow field cell when the target appears in the narrow field ofview, thus providing greater sensitivity and discrimination againstsources of extraneous radiation that are not in the narrow field ofview. Furthermore, the signal processing circuit has a narrow bandpasscharacteristic to exclude extraneous signals due to radiation sourcesother than that on the missile. The signal processing circuit developssteering signals that are transmitted to the missile, causing it tofollow the line-of-sight to the target.

An embodiment of an automatic missile guidance system, in accordancewith the present invention, is shown pictorially in FIG. 1 andfunctionally in FIG. 2. A portable guidance unit is provided that may besimilar in size and appearance to a rifle stock. The guidance unit 20 ispointed or aimed toward a target 21 and automatically provides steeringsignals to a groundlaunched, self-propelled missile 22 to direct ittoward the target 21. The guidance unit 20 includes a visual telescope23 mounted to a gun stock 24 for use by a human operator to establish aline-of-sight 25 between the guidance unit 20 and the target 21. Aninfrared telescope 26 is also disposed on the gun stock 24 and alignedwith the visual telescope 23 for intercepting pulsating infraredradiation from the missile 22 and detecting deviations of the missile 22from the line-ofsight 25. Inasmuch as the infrared telescope 26 and thevisual telescope 23 are side by side, their optical axes cannot beexactly coincident. However, the few inches difference between the axesmake little difference in the operation of the system and the axes mayactually intersect at or near the target 21. The forward portion 27 ofthe guidance unit 20 contains a signal processing circuit that developssteering signals and transmits them to the missile 22 via a cable 30, abox 31 containing missile launching and signal translation circuits, andvia wires 32 trailing behind the missile 22.

The gun stock 24 may be of the type normally used for rifles, butmodified for the purpose at hand. A folding bipod 28, about which theassembly can pivot, provides a forward support. It will be apparent thatother convenient arrangements may be used in place of the gun stock 24.For example, the guidance unit 20 may be mounted to a tripod in a mannersuch that it may be easily carried and easily pointed in any direction.The visual telescope 23 may have a variable power and may be of the typenormally used as a telescopic sight on a rifle, having cross hairs inthe center of the field of view.

The missile 22 may be any remotely guided type, such as the NordAviation 88-] l-A-l, for example, which is described in the NordAviation brochure 58-1 1 Teleguided Missile Type 5210". This missile 22receives its guidance signals over wires 32 trailing behind the missile22. However, the automatic missile guidance system of the presentinvention is not restricted to use with this particular missile 22, andmay be easily adapted for use with a missile that receives its guidancesignals in some other way as, for example, by radio transmission.

Although the missile 22 itself is not part of the present invention, theoutside configuration of the missile 22 is shown in FIGS. 3 and 4 toillustrate how the present invention is adapted for use therewith. Themissile 22 is initially propelled for a short time by a booster rocketmotor which discharges through nozzles 40 and 41 disposed on oppositesides of the missile 22 near the aft end thereof, and is subsequentlypropelled for the remainder of the flight by a sustainer rocket motor.The sustainer motor nozzle is not shown in FIGS. 3 and 4, but iscentrally located in the aft end of the missile 22. Control momentsresult from solenoid-actuated spoilers operating in the exit area of thesustainer nozzle. The spoilers oscillate continuously and, bycontrolling the spoiler duty cycle, proportional control is achieved.Guidance signals are received by the missile 22 through the wires 32connected to the box 31, which may be representative of the Nord T-9generator, for example, and which contains missile firing circuits andcircuits for converting guidance signals into the form best adapted fortransmission to the missile 22. The box 31 may also contain manualguidance arrangements. On the missile 22, the wires 32 are initiallycontained in two bobbins disposed in bobbin cases 42 and 43 disposed onopposite sides of the missile 22 near the aft end thereof. The wires 32are unreeled during flight of the missile 22. Since the missile 22 isintentionally rolled during flight, the guidance signals are resolvedinto pitch and yaw commands by a vertical gyro and a four-segmentcommutator. The near ends of the guidance wires 32 are attached to ananchor block 44 initially attached to the rear of the missile 22, asseen in FIGS. 3 and 4, but left behind as the missile 22 is launched, asshown in FIG. 1. i

In accordance with the present invention, the missile 22 is providedwith an interrupted radiation source 50, disposed on the aft endthereof, that generates distinctive infrared radiation pulsating at aconstant frequency. As will be fully described hereinafter, pulsation iscaused by an interrupter operated by a battery 51, also located on theaft end of the missile 22. The battery 51 is connected to the source 50when the missile 22 separates from the block 44. The interruptedinfrared radiation source 50 is shown in FIGS. 5 and 6 and comprises acylindrical housing 52 filled with a pyrotechnic composition 53 thatproduces a thermite reaction when ignited. A suitable mixture for thepyrotechnic composition 53 may be, for example, iron ozide, 56 percent(by weight); aluminum powder, 14 percent; boron, 3 percent; and bariumchromate, 27 percent. Another suitable mixture is molybdic trioxide,percent and aluminum powder, 20 percent. Other mixtures may also befound to be satisfactory. An electrically operated firing squib 54 isdisposed inside the case 52 in contact with pyrotechnic composition 53.The radiating surface is a molybdenum disk 55, having a zirconiumcarbide coating and which is disposed near one end of the housing 52. Atleast one heavy metal bar 56 is embedded in the pyrotechnic composition53 to produce a hot metal mass that beats the molybdenum disk 55 whenthe radiation source 50 is ignited. The bar 56 may be made of iron ormay be made of percent tungsten and 10 percent copper or nickel, forexample.

The radiant energy from the molybdenum disk 55 is interrupted by arotating disk 58, similar to a butterfly valve, and rotatably securedadjacent the molybdenum disk 55. The butterfly disk 58 is mechanicallycoupled at the circumference thereof to the shaft of a direct currentmotor 57, having a regulated speed which, in the present example, is 100revolutions per second. The motor 57 is secured to the housing 52 of theradiation source 50. As the butterfly disk 58 rotates, it interrupts theradiation from the molybdenum disk 55 twice each revolution to produceinterrupted infrared radiation pulsating at a frequency of 200 cyclesper second.

It will be understood that other types of sources ofinterruptedradiation may be utilized, if desired. For example, an intense electriclamp, having an interrupter, produces pulsating radiation suitable foruse in a system, according to the present invention. Additionally,mechanical devices may be employed to cause pulsation of the plume ofexhaust gases from the rocket motor or a portion of these gases that isbypassed to a separate outlet.

The infrared telescope 26, shown in FIG. 7, has a generally cylindricalouter case 60, with an entrance aperture 61 at one end to admit radiantenergy. A window 62 is disposed in the entrance aperture 61 and may, ifdesired, have a multilayer interference filter deposited on the innersurface to pass only radiation having wavelengths within a desired band.Adjacent the window 62 are first and second objective lenses 63 and 64that focus intercepted radiant energy onto a fiat surface of adisk-shaped reticle 65 disposed transversely to and concentric with theoptical axis of the objective lenses 63 and 64.

Adjacent to the reticle 65 is a condensing lens 66. A large radiantenergy detector 67 is disposed adjacent and generally parallel theretoin the end of the infrared telescope case 60, opposite the entranceaperture 61. The condensing lens 66, in effect, focuses the image of theentrance aperture 61, as seen through the first and second objectivelenses 63 and 64 and the reticle 65, onto the large radiant energydetector 67, and, thus, the radiant energy passing through thecondensing lens 66 more or less uniformly illuminates the large radiantenergy detector 67. A large radiant energy detector is required so thatradiant energy from the sun or other intense sources of backgroundradiation, which may lie within the large field of view of the infraredtelescope 26 will not saturate the signal generating capability of thedetector and is also required by a law of geometrical optics, known asthe Abbe sine condition, which states, in effect, that for any givenfield of view, there is a minimum size, increasing with the size of thefield of view, for the image of the entrance aperture 61 that can befocused by the condensing lens 66 onto a detector. Both these conditionsare met, in the present example, by the large, radiant energy detector67, which is approximately 3'inches on a side. A detection cell of thissize is normally a cell blank from which smaller cells are ordinarilycut, or several cell blanks placed side by side.

In the center of the condensing lens 66, concentric with the opticalaxis of the lenses 63, 64 and 66, is located a generally cylindricallight pipe 68, having a small radiant energy detector 70 disposed at theend thereof. The internal shape of the light pipe 68 is that of ahollow, truncated cone, the larger diameter end being flush with thesurface of the condensing lens 66 adjacent the reticle 65. The smallerinternal diameter end of the light pipe 68 extends away from the reticle65 and through the opposite surface of the condensing lens 66. Theinternal surface of the light pipe 68 is highly polished and the smallradiant energy detector 70 is disposed at the small diameter end of thelight pipe 68. Energy intercepted by the light pipe 68 is directed tothe small detector 70 by reflection from the inner surface of the lightpipe 68. Thus, the light pipe 68 acts as a condensing lens toconcentrate diverging energy passing through the reticle 65 onto thesmall detector 70.

The optical elements of the infrared telescope 26 may be made of anymaterial that is transparent to the radiant energy of interest and has asuitable index of refraction. For intercepted radiant energy in theinfrared spectrum, silicon or sapphire, for example, may be used. Lensesfor use in the infrared spectrum may be opaque to visible light. Theradiant energy detectors 67 and 70 may be made of any suitable materialfor converting radiant energy in the spectrum of interest into anelectrical signal. In the present embodiment of the invention, leadsulfide, for example, will be found satisfactory. Although the presentinvention is described with reference to operation with radiant energyin the infrared portion of the radiant energy spectrum, it is to beexpressly understood that the apparatus may be easily adapted for usewith radiant energy in other parts of the radiant energy spectrum, suchas in the visible or ultraviolet portion, for example. This may be doneby proper selection of the lens materials and of the radiant energydetectors 67 and 70, in accordance with well-known principles.

The field of view of the infrared telescope 26 is 40 degrees. Images ofsources of radiant energy formed on the reticle 65 by the objectivelenses 63 and 64 are small and sharply defined in the central portion ofthe reticle 65. However, sources near the outer edge of the field ofview form images near the circumference of the reticle 65 that areslightly out of focus and, consequently, larger and somewhat blurred.Inasmuch as accuracy is required only on or near the optical axis of theinfrared telescope 26, the blurring ofimages distant from the opticalaxis is not deleterious to the operation of the system.

It will be apparent that the major portion of the optical field of viewof the infrared telescope 26 is intercepted by the large radiant energydetector 67. However, the small radiant energy detector 70 interceptsthe central 6 degrees of the optical field of view. Thus, the infraredtelescope 26 has dual concentric radiant energy detectors 67 and 70, oneproviding a wide field of view and the other providing a narrow field ofview.

The reticle 65 amplitude modulates intercepted radiant energy in amanner that will be fully described hereinafter. The reticle 65 is aflat disk made of a material that is transparent to radiation in thespectrum of interest, but has a partially opaque modulating patternsuperimposed thereon. The reticle 65 is rotated to produce themodulation, and for this purpose, is mounted at its circumference in agenerally cylindrical holder 72. An internal projection 73 of theinfrared telescope case 60 rotatably supports the reticle holder 72 bymeans of ball bearings 74 that engage the inner surface of the holder72. A ring gear 75 is disposed on the outside of the reticle holder 72.An electric motor 76 disposed outside the infrared telescope case 60 hasa shaft 77 projecting into the case 60, to which is attached a drivinggear 78 that is meshed with the ring gear 75. In this manner, the motor76 causes the reticle 65 to rotate about its center, which is on theoptical axis of the objective lenses 63 and 64. The reticle 65 isrotated at a constant rate of 18 revolutions per second in the presentexample.

The reticle 65 has associated with it an arrangement for producing phasereference signals indicative of the instantaneous angular position ofthe reticle 65. For this purpose, the reticle holder 72 is provided witha band 80 around the outside thereof, adjacent the ring gear 75. Theband 80 is made of magnetic material, such as steel, while the reticleholder 72 is made of nonmagnetic material, such as aluminum. The band 80tapers in width from a maximum width point 81 (FIG. 7), to a minimumwidth point 82. The band 80 tapers linearly and the maximum point 81 isdiametrically opposite the minimum point 82. A first coil and magnetassembly 79 is provided, with a first pole piece 83 fastened to theouter case 60 of the infrared telescope 26 adjacent and extending towardthe reticle holder 72 and spaced slightly away from the band 80. Apermanent bar magnet 84 extends out from the pole piece 83 and has woundaround it a wire coil 85. Referring to FIG. 8, a second pole piece 86 isat the other side of the magnet 84 and also extends toward the bank 80.The faces of the pole pieces 83 and 86 are as broad as the width of theband 80 at the maximum point 81. The case 60 that encloses the phasereference signal coil and magnet assembly 79 is nonmagnetic.

Thus, the magnet 84 has a magnetic circuit that extends from one pole ofthe magnet 84 through the as sociated pole piece 83, through a portionof the band 80 on the reticle holder 72, through the second pole piece86 to the remaining pole of the magnet 84. As the reticle holder 72rotates, the width of the band 80 in the magnetic circuit of the magnet84 varies, so that a variable reluctance path exists between the polesof the magnet 84. This, in turn, causes a potential to be developed inthe coil 85 around the magnet 84. Hence, as the reticle holder 72 andreticle 65 rotate, a periodic signal is generated in the coil 85, whosephase is directly related to the instantaneous angular position of thereticle holder 72. A second coil and magnet assembly 87 (FIG. 8),similar to the first, is located in a position 90 displaced from thefirst coil and magnet assembly 79 and produces a second phase referencesignal that is displaced 90 degrees in phase from the first phasereference signal.

The modulation pattern superimposed on reticle 65, and shown in FIG. 9,is opaque to radiation in the spectrum of interest. The pattern can beconsidered to consist of a series of adjacent, concentric, circularbands. Each band is divided into two parts, one part of which is opaqueand the other part remaining transparent, by a circle that is notconcentric with the center of the pattern. The area in each band betweenthe outer boundary circle and the dividing circle is opaque, and thearea between the dividing circle and the inner boundary circle istransparent. In the outer part of the reticle 65, the dividing circle ineach band is tangent with the outer boundary circle in a maximumtransmission zone and tangent with the inner boundary circle in aminimum transmission zone 91, 180 away from the maximum. In the innerportion of the reticle 65, the dividing circle is not tangent to eitherthe inner or outer boundary circles, but the separation between thedividing circle and the outer boundary circle in the maximumtransmission zone 90 is equal to the separation between the dividingcircle and the inner boundary circle in the minimum transmission zone91. Furthermore, in the inner portion of the reticle 65, the circularbands themselves are narrower than in the outer portion.

Thus, the pattern comprises concentric, circular, opaque lines thatprogressively increase in width around the reticle 65 from a minimumwidth in the maximum transmission zone 90 to a maximum width in theminimum transmission zone 91 and decrease again to the minimum width.The size of the image focused on the reticle 65 is larger than the widthof the circular bands. The bands near the center of the reticle 65 arenarrower than the outer bands, since the image size is smaller near thecenter. Since the image is larger than the bands, the radiant energytransmitted by the reticle 65 is amplitude modulated in a sinusoidalfashion as the reticle 65 is rotated.

The reticle pattern is not uniform over the entire surface of thereticle 65, as may be seen in FIG. 9, but is divided into three distinctconcentric regions having slightly different modulation characteristics.The central portion of the field of view of the infrared telescope 26,extending from the optical axis to a circle 1 away therefrom, falls on aregion of the reticle 65 where the pattern comprises closely spacedopaque lines that provide a modulation percentage varying from zeropercent modulation at the center to 50 percent modulation at thecircumference thereof. That is, radiant energy producing an image at thecenter of the reticle 65 passes through the reticle 65 unmodulated, andradiant energy producing an image l away from the center of the reticle65 is only 50 percent intercepted or modulated by the opaque pattern inthe minimum transmis' sion zone 91. The portion of the optical field ofview that extends between 1 and 6 from the optical axis falls on asecond region of the reticle in which the opaque lines are not quite asclosely spaced as in the first or central region, and in which thepercent modulation varies from 50 percent to percent as the angulardistance from the center of the pattern increases. The third or outerregion has opaque lines spaced farther apart than the other two regions,and in which the modulation is 100 percent throughout. The modulationcharacteristic of the reticle is illustrated graphically in FIG. 10,where percent modulation is plotted along the ordinate, as a function ofthe angular distance from the center of the reticle in degrees along theabscissa.

It will be apparent from the graph of FIG. 10 that the percentage ofmodulation of radiant energy from the radiation source 50 on the guidedmissile 22 is a function of the angular distance from the optical axisof the image thereof. Accordingly, the amplitude of the modulation isindicative of the angular deviation of the missile 22 from theline-of-sight 25. Furthermore, the closer the image is to the opticalaxis of the infrared telescope 26, the greater is the amount ofmodulation produced per unit of angular deviation. This is indicated bythe steep slope of the curve of FIG. 10, as it passes through zero.Accordingly, the subsequent control circuits do not need to have anextremely high gain and the noise in the system is maintained atacceptable levels, due to a relatively large deviation signal beingprovided, even when the deviation is small.

The opaque pattern may be applied to the reticle 65 by various methods.One process that has been found satisfactory is a photographic processin which the surface of the reticle 65 to which the pattern is to beapplied is first silvered and then coated with a photo-resist material.An image of the pattern is focused on the surface of the reticle 65,after which the reticle 65 is placed in an etchant bath, where portionsof the silvered area are etched away to leave the opaque pattern.

FIG. 11 shows a circuit diagram in block form of an embodiment of asignal-processing circuit, in accordance with the present invention. Inthis circuit, the radiant energy from the source 50 on the missile 22intercepted by the infrared telescope 26 is converted into guidancesignals that are transmitted to the missile 22. As mentioned previously,the interrupted radiation source 50 on the missile 22 emits radiantenergy pulsating at 200 cycles per second. Pulsating radiant energyintercepted by the infrared telescope 26 is amplitude modulated by thereticle 65 at 18 cycles per second and falls on the radiant energydetectors 67 and 70. The modulated, pulsating radiant energy isconverted to an amplitude-modulated electrical carrier wave, or trackingsignal, by the detectors 67 and 70. The carrier wave frequency is 200cycles per second and the modulating wave frequency is 18 cycles persecond, so that the tracking signal occupies a frequency band from182-218 cycles per second.

Electrical signals from the small radiant energy detector 70 are appliedto a preamplifier 100 for amplification. The preamplifier 100 may be anylow noise amplifier circuit having a bandwidth of approximately 150-300cycles per second. Electrical signals from the large radiant energydetector 67 are also applied to the input of a preamplifier 101, whichmay be identical to the preamplifier 100 associated with the smalldetector 70. Output signals from the preamplifiers 100, 101 are appliedto a single-pole, double-throw relay 102, the small cell preamplifier100 being connected to the normally open contact 103 and the large cellpreamplifier 101 being connected to the normally closed contact 104.Thus, either the signal from the small detector 70 or the signal fromthe large detector 67 appears at the switch arm 105, depending uponwhether the switching relay 102 is energized or de-energized. Thepreamplifiers 100, 101 are phase compensated to provide identicalamounts of phase shift to signals amplified thereby. Accordingly, whenthe relay 102 switches between the outputs of the preamplifiers 100,101, there will be no phase discontinuity in the tracking signal.

A circuit is provided for automatically controlling the switching of therelay 102. The output of the small cell preamplifier 100 is connected tothe input of a narrowband amplifier 107. The bandwith of this amplifier107 is from approximately 175 to 225 cycles per second, so that it isresponsive only to the tracking signal derived from the radiation fromthe missile 22. Inasmuch as background radiation is not pulsating at 200cycles per second, the electrical signal resulting therefrom isdiscriminated against by the narrowband amplifier 107, because itsfrequency is outside the passband thereof. The output signal of thenarrowband amplifier 107 is applied to a rectifier and filter 108 thatdevelops a direct-current voltage which is applied to the input of aswitch amplifier 110. The relay 102 has its energizing coil connected tothe output of the switch amplifier 1 10.

The relay 102 is normally not energized and, in this condition, theswitch arm 105 is connected to the large detector 67. When a signal ofsufficient amplitude and having a frequency in the band from 175 to 225cycles per second appears at the output of the small detector 70, it isamplified, rectified and applied to the switch amplifier 110, whichenergizes the relay 102. Subsequently, if the signal from the smalldetector 70 falls below a predetermined amplitude, the relay 102 isdeenergized. Thus, when the missile 22 is in the narrow 6 field of viewof the small detector 70, the relay 102 automatically switches to thesmall detector 70, and switches back again when the missile 22 leavesthe field of view of the small detector 70.

To prevent rapid switching back and forth of the relay 102 when themissile 22 momentarily passes through the field of view of the smalldetector 70, the rectifier and filter 108 is provided with a suitabletime constant. Thus, the missile 22 must be in the field of view of thesmall detector 70 for a predetermined length of time before the voltageat the output of the rectifier and filter 108 can increase to the levelat which switching takes place. Similarly, when the missile 22 leavesthe field of view of the small detector 70, the voltage at the output ofthe rectifier and filter 108 gradually decreases to the switching level.The switch amplifier 110 is biased to have a suitable threshold level,so that when the applied voltage is above the threshold, the relay 102is energized and, when the applied voltage is below the threshold, therelay 102 is deenergized.

When the missile 22 is close to the target 21, the relay 102 is lockedinto the energized position. This is accomplished by means of a switchcontrol voltage source 111 that applies a voltage that exceeds thethreshold level to the input of the switch amplifier 110 at the end ofapredetermined time interval. The switch control voltage source 111 is acapacitor-charging circuit that begins operation at the time the missile22 is fired. After 6.7 seconds, the potential at the output of theswitch control voltage source 111 exceeds the threshold level, causingthe relay 102 to be locked into the energized position;

The switch arm 105 of the relay 102 is connected to the input circuit ofa second narrowband amplifier 112 that is similar to the narrowbandamplifier 107 in the relay control circuit. Specifically, the narrowbandamplifier 112 has a bandwidth of to 225 cycles per second to pass onlythe tracking signal while excluding background signals. An AGC(Automatic Gain Control) circuit 113 is connected to the narrowbandamplifier 112. This circuit 113 rectifies and filters the trackingsignal appearing at the output of the narrowband amplifier 112 todevelop an AGC voltage that is applied to the narrowband amplifier 112to control the gain thereof. Thus, as long as the missile 22 is in thefield of view of the infrared telescope 26, the tracking signalappearing at the output of the narrowband amplifier 112 has asubstantially constant amplitude.

A demodulator 114 is also connected to the output of the narrowbandamplifier 1 12 and comprises a rectifier and filter that demodulates thetracking signal to recover the 18-cycle-per-second modulating wave orerror signal introduced by the reticle 65. The error signal is appliedto the input circuit of a variable gain amplifier 115 that increases theamplitude of the missile error signal as the missile 22 approaches thetarget 21 to account for the increasing distance between the guidanceunit and the missile 22. if this were not done, the inissile 22 wouldundercorrect for errors as it approached the target 21. Accordingly, thegain of the variable gain amplifier 115 is gradually increasedthroughout the time of flight, in accordance with the graphicalrepresentation shown in FIG. 12, in which the gain of the amplifier 115is plotted along the ordinate as a function of elapsed missile flighttime plotted along the abscissa.

The variable gain amplifier 115 is an amplifier having a negativefeedback loop, including a resistive voltage divider network. A pair ofdiodes connect a relatively low resistance in shunt with a portion ofthe feedback network. The diodes are normally biased to benonconductive, at which time the negative feedback is large and the gainof the amplifier 115 is low. When the diodes become conductive, theimpedance of the feedback network is decreased, which decreases thenegative feedback and the gain of the amplifier 115 increases. The gainof the variable gain amplifier 115 is controlled by a gain controlvoltage source 116, which is similar to the switch control voltagesource 111 of the signal switching circuit. The gain control voltagesource 116 includes a capacitor charging circuit that is set intooperation when the missile 22 is fired. The exponential charging voltageis applied to the diodes in the feedback network of the variable gainamplifier 115 to cause them to gradually become more and more conductiveas the charging voltage increases.

The error voltage from the output of the variable gain amplifier 115 isapplied to a pair of circuits that develop steering signals. Thesecircuits are a pitch phase detector 117 and a yaw phase detector 118,which may be conventional phase detector circuits. Reference signals forthe pitch and yaw phase detectors 117 and 118 are derived from the coiland magnet assemblies 79 and 87 associated with the reticle holder 72,previously described. These coil and magnet assemblies 79 and 87 developperiodic wave reference signals that are 90 displaced in phase withrespect to each other, and have a fixed phase relationship to theangular position of the reticle holder 72. The pitch and yaw referencesignals are applied to squaring circuits 120 and 121 that amplify andclip the reference signals to develop square waves that are then appliedto the pitch and yaw phase detectors 117 and 118.

To establish the proper phase relationship between the modulationpattern on the reticle 65 and the pitch and yaw reference signals, animage of the radiation source 50 is focused on the reticle 65 at aposition vertically displaced from the center of the reticle 65. The

angular position of the reticle 65, with respect to the reticle holder72, is manually adjusted until the yaw phase detector 118 provides nosteering signal output and the pitch phase detector 117 provides amaximum steering signal output when the guidance unit 20 is operating.When the image is moved to a position laterally displaced from thecenter of the reticle 65, the pitch phase detector 117 provides nosteering signal output and the yaw phase detector 1 18 provides amaximum steering signal output.

The output circuits of the pitch and yaw phase detectors 117, 118 areeach connected to corresponding pitch and yaw compensation networks 122,123 that provide stability and damping, in accordance with wellknownprinciples of feedback control systems. That is, the compensationnetworks 122 and 123 modify the natural response of the guidance systemto disturbances thereof by means of such well-known techniques as basiclead compensation and error rate damping, for example. The compensationnetworks 122, 123 are specifically adapted to the type of missile 22with which the guidance system is to be used. This compensation providesguidance system stability and satisfactory transient response,regardless of displace ments of the missile 22 from the line-of-sight 25at launch and internal system noise, for example. In addition, a gravitybias may be provided to prevent collision of the missile 22 with theground during overshoots around the line-of-sight 25.

The output of the pitch and yaw compensation networks 122, 123 areconnected to a steering signal trans mission circuit 124 which appliesthe steering signal to the missile 22. The steering signal transmissioncircuit is, in the present example, a box 31, shown in FIG. 1, which isrepresentative of the Nord T-9 generator and which contains firing andsignal conversion circuits and to which are connected the wires 32trailing behind the missile. It will be understood that the steeringsignal transmission circuit 124 may be any other form of guidancecommand link, such as a radio circuit.

In operation, the portable guidance unit 20 is aimed toward the target21 by the operator who sights through the visual telescope 23. Theoperator maintains the portable guidance unit 20 trained on the target21 at all times during the flight of the missile 22, even if the target21 is moving. This establishes a lineof-sight 25 between the guidanceunit 20 and the target 21. The missile 22 is then launched into thefield of view of the infrared telescope 26. The launching process setsinto operation the interrupted radiation source on the rear of themissile 22, which emits infrared energy pulsating at 200 cycles persecond. The launching of the missile 22 also sets into operation thecharging of capacitors in the switch control voltage source 111 and thegain control voltage source 116.

The pulsating radiant energy from the missile 22 is intercepted by theinfrared telescope 26 where it is focused on the reticle 65. The reticlemodulates the intercepted radiant energy at 18 cycles per second, thephase of the modulating signal being dependent upon the angulardirection of the missile 22 from the line-ofsight 25. The amplitude ofthe modulating signal is dependent upon the radial distance of themissile 22 from the line-of-sight 25. The modulated intercepted radiantenergy is then concentrated on the radiant energy detectors 67 and 70,which convert the radiant energy into an amplitude-modulated electricalcarrier wave.

It will be apparent that background radiation from objects other thanthe missile 22 and including the sun, do not result in a similarelectrical signal because the radiant energy emitted by backgroundobjects is not pulsating at 200 cycles per second. However, backgroundradiation will be modulated to some extent at 18 cycles per second bythe reticle 65. Signals from the radiant energy detectors 67 and 70 areapplied to the preamplifiers 100, 101, which have a bandwidth of 150 to300 cycles per second and, therefore, will not pass electrical signalsat 18 cycles per second that are derived from background radiation.

Even when intense sources of background radiation, such as the sun, arein the field of view, the large detector 67 is not saturated. Thus, thepulsating energy from the missile 22 continues to produce electricalsignals at the output of the large detector 67. Accordingly, the missilesignal is at all times distinguishable from background signals.

The amplitude modulated electrical carrier wave, or tracking signal,then passes through the contacts of the relay 102 to the input of thenarrowband amplifier 112, which further discriminates against extraneoussignals. The AGC circuit 113, associated with the narrowband amplifier112, maintains the tracking signal at a substantially constant amplitudeat the output of the narrow band amplifier 112. However, it will beunderstood that the time constant is sufficiently long so that themodulation will not be suppressed by gain control action. The trackingsignal is then applied to the demodulator 114, where it is demodulatedto recover the 18- cycle-per-second modulating wave or error signalintroduced by the reticle 65. The phase of the error signal is afunction of the angular direction of the image from the center of thereticle 65 and the amplitude of the error signal is a function of theradial distance of the image from the center of the reticle 65.

The error signal is applied to the input of the variable gain amplifier115, which adjusts the amplitude of the error signal to account for theincreasing distance of the missile 22 from the guidance unit. The errorsignal is then applied to the pitch and yaw phase detectors 117 and 118,which convert the error signal from polar form into rectangular form bymeans of the phase reference signals developed by the coil and magnetassemblies 79 and 87 associated with the reticle 65. This operationresults in a pitch steering signal at the output of the yaw phasedetector 118. The pitch and yaw steering signals are then applied to thepitch and yaw compensation networks 122 and 123, which provide guidancesystem stability. The steering signals are then applied to the steeringsignal transmission circuit 124, where they are transmitted to themissile 22 to correct for deviations thereof from the line-of-sight 25.

Inasmuch as this is a closed loop system, the missile 22 always tends tofollow the line-of-sight 25. If the missile 22 is not on theline-of-sight 25 at launch, the error signal produced steers the missile22 back onto the line-of-sight 25 because the system operates to reducethe error signal and the steering signals to zero.

Initially, the missile 22 may have a large heading error, with respectto the line-of-sight 25. However, the extremely wide field of view ofthe infrared telescope 26 intercepts the pulsating radiation from themissile 22 and initiates the controlling signals to bring it back to theline-of-sight 25. As the missile approaches the line-of-sight 25, itenters the central 6 of the field of view of the infrared telescope 26,at which time the pulsating infrared radiation falls on the smallradiant energy detector 70. The result is that the tracking signal isapplied to the narrow-band amplifier 107 in the signal switchingcircuit, which discriminates against background signals and applies itto a rectifier and filter 108 that, after a short time interval, buildsup a voltage that exceeds the threshold of the switch amplifier 110,causing the relay 102 to connect the output of the small detector intothe guidance system.

The narrow field of view of the small detector 70 eliminates manysources of background radiation and, therefore, provides increaseddiscrimination against background signals. The small detector 70 alsoprovides greater sensitivity. Should the missile 22 leave the central 6of the field of view of the infrared telescope 26, the voltage at theoutput of the rectifier and filter 108 decreases after a short timeinterval to a value less than the threshold level of the switchamplifier 110, at which time the large detector 67 is connected into theguidance loop by the relay 102. 6.7 seconds from the time of missilelaunch, the gradually increasing voltage from the switch control voltagesource 111 exceeds the threshold of the switch amplifier and locks thesmall detector 70 into the guidance loop as, at that time, the missile22 should be within the central 6 of the field of view of the infraredtelescope 26.

When the image is on the central 1 degree of the reticle 65, the errorsignal is larger per unit of angular deviation from the center of thereticle 65. Thus, the signal processing circuit does not need to have anextremely high gain.

As the missile 22 approaches the target 21, the gradually increasingvoltage at the output of the gain control voltage source 116 causes thegain of the variable gain amplifier 115 to gradually increase, therebyincreasing the amplitude of the error signal, so that the missile 22does not undercorrect for errors as it approaches the target 21.

Thus, there has been described an automatic missile guidance system thatis small in size, light in weight, relatively inexpensive, and simple tooperate. The missile guidance system of the present invention includesinfrared tracking equipment of a simple, yet effective type, that isrelatively insensitive to background radiation from the sun and otherintense sources.

What is claimed is:

1. An automatic missile guidance system for guiding a missile along aline-of-sight to a target established by a human operator, said missilehaving guidance means comprising:

a guidance unit for developing steering signals related to the deviationof said missile from said lineof-sight;

means for transmitting said guidance signals from said guidance unit tosaid missile; and

a source of pulsating radiant energy on said missile and directed to therear thereof, said source of radiant energy having a predeterminedpulsation frequency, said guidance unit being selectively responsive tosaid radiant energy at said predetermined pulsation frequency.

2. The automatic missile guidance system of claim 1 wherein saidguidance unit has means for narrowing its field of view when saidmissile is proximate to said lineof-sight.

3. The automatic missile guidance system of claim 2 wherein saidguidance unit has a radiant energy receiver thereon adapted to receiveradiant energy from said source of pulsating radiant energy on saidmissile, said radiant energy receiving means having a large radiantenergy detector disposed therein to receive radiant energy in any partof the field of view and a small radiant energy detector disposedtherein, said small radiant energy detector being positioned to receiveradiant energy in the central portion of the field of view of saidradiant energy receiver, and switch means for switching between saidlarge and said small radiant energy detectors in response to position ofmissile source image in field of view.

4. The automatic missile guidance system of claim 3 wherein said smallradiant energy detector means has an output to said switch means toswitch said switch means so that its small radiant energy detector meansis switched to control said missile when the input radiance to saidsmall radiant energy detection means exceeds a predetermined value.

5. The automatic missile guidance system of claim 4 wherein said sourceof pulsating radiant energy on said missile operates at a substantiallyconstant frequency.

6. The automatic missile guidance system of claim 5 wherein said radiantenergy receiving means on said guidance unit comprises a telescopehaving a wide field of view about an optical axis, a reticle disposed atthe focus of said telescope concentric with and transverse to the axisthereof, means rotating said reticle about the axis of said telescope ata predetermined speed, said reticle having an opaque modulation patternthereon to provide a substantially sinusoidally varying averagetransmissivity gradient circularly around said reticle and to provide arapidly increasing depth-of-modulation gradient outward from the centerof said reticle, said large radiant energy detector being disposed toreceive radiant energy passed by said reticle, said small radiant energydetector being disposed in a position to intercept radiant energypassing through the central portion of said reticle.

7. The automatic missile guidance system of claim 3 wherein the outputof said switch is connected to first and second phase detectors, forrespectively detecting pitch and yaw of said missile, said phasedetectors being connected to said missile to guide said missile.

8. The automatic missile guidance system of claim 7 wherein said meansfor transmitting said guidance signals from said guidance unit to saidmissile comprises at least one wire interconnected between said guidanceunit and said missile.

9. An automatic missile guidance system for guiding a missile along aline-of-sight to a target established by a human operator, said missilehaving guidance means comprising:

a guidance unit for developing steering signals related to the deviationof said missile from said lineof-sight;

means for transmitting said guidance signals from said guidance unit tosaid missile; and

a source of pulsating radiant energy on said missile and directed to therear thereof, said source of radiant energy having a predeterminedsubstantially constant pulsation frequency, said guidance unit beingselectively responsive to said radiant energy at said predeterminedsubstantially constant pulsation frequency, said guidance unit havingmeans for narrowing its field of view when said missile is proximate tosaid line-of-sight.

10. A system for guiding a self-propelled missile having steering meanscomprising:

means disposed on said missile for emitting radiant energy pulsating ata predetermined frequency rearwardly thereof;

means for intercepting radiant energy having a wide field of view;

means disposed within said interception means for amplitude modulatingintercepted radiant energy at a predetermined frequency;

a large radiant energy detector disposed to receive radiant energyintercepted by said interception means and modulated by said modulationmeans;

a small radiant energy detector disposed within said interception meansin a position to receive radiant energy in the central portion of thefield of view of said interception means and modulated by saidmodulation means;

switch means having inputs electrically coupled to said radiant energydetectors and normally passing to its output only signals appearing atthe output of said large radiant energy detector, said switch meansbeing responsive to a switching signal applied at a control input forpassing to its output only signals appearing at the output of said smallradiant energy detector;

first frequency selective means having its input electrically coupled tosaid small radiant energy detector and having a narrow frequencypassband centered around said predetermined frequency, said switch meanshaving its control input electrically coupled to the output of saidfirst frequency selective means;

second frequency selective means having its input coupled to the outputof said switch means and having a narrow frequency passband centeredaround said predetermined frequency;

an amplitude modulation demodulator having its input coupled to theoutput of said second frequency selective means;

phase detecting means having an input coupled to the output of saiddemodulator;

reference means associated with said modulation means for developingperiodic reference signals, the phase of which is related to the phaseof said modulation means, said reference signals being coupled to thereference input of said phase detecting means; and

signal transmission means having its input coupled to the outputs ofsaid phase detecting means and its output coupled to said missile.

11. A guided missile system comprising:

a self-propelled missile having steering means;

a source of infrared energy pulsating at a substantially constantpredetermined frequency disposed on said missile and directed rearwardlythereof;

a visual telescope having an optical axis;

an infrared telescope having an optical axis substantially aligned withthe optical axis of said visual telescope and having a wide field ofview;

a reticle disposed at the focus of said infrared telescope concentricwith and transverse to the axis thereof;

means for rotating said reticle about the axis of said infraredtelescope at a predetermined speed, said reticle being transparent tosaid pulsating infrared energy and having an opaque coating arranged ina modulation pattern thereon, said coating being disposed in asinusoidally varying concentration circularly around said reticle toprovide a sinusoidal average transmissivity gradient circularly aroundsaid reticle, said coating being disposed in a varying radialconcentration increasing outwardly to provide a rapidly increasingdepth-of-modulation gradient near the center of said reticle;

a condensing lens disposed adjacent said reticle;

a large radiant energy detector disposed to receive radiant energyintercepted by said infrared telescope and passed by said reticle andsaid condensing lens;

a light pipe disposed in the center of said condensing lens to interceptradiant energy passing through the central portion of said reticle;

a small radiant energy detector disposed in said light pipe in aposition to receive radiant energy intercepted thereby;

an electromagnetic relay having a normally open contact;

a normally closed contact;

a switch arm and an actuating coil, said small radiant energy detectorbeing electrically coupled to the normally open contact of said relay,said large radiant energy detector being electrically coupled to thenormally closed contact of said relay;

a first narrowband amplifier having its input electrically coupled tosaid small radiant energy detector and having a narrow passband centeredaround said predetermined frequency;

a rectifier and filter connected to the output of said first narrowbandamplifier, said filter having a predetermined charge and discharge timeconstant;

a switch amplifier having its input electrically coupled to the outputof said rectifier and filter and having its output connected to theactuating coil of said relay, said switch amplifier being biased to havea predetermined input threshold level above which said relay isenergized and below which said relay is de-energized;

a source of voltage that exceeds said threshold a predetermined timeafter the launching of said missile electrically coupled to the input ofsaid switch amplifier;

a second narrowband amplifier having its input coupled to the switch armof said relay and having a narrow passband centered around saidpredetermined frequency;

an automatic gain control circuit coupled to said second narrowbandamplifier for maintaining plitude;

an amplitude modulation demodulator having its input coupled to theoutput of said second narrowband amplifier;

a variable gain amplifier having its input coupled to the output of saiddemodulator, said variable gain amplifier having a gain that varies as afunction of an applied control voltage;

a gain control voltage source coupled to said variable gain amplifierand applying a control voltage thereto that gradually increases the gainof said variable gain amplifier from the time said missile is launched;

a pair of phase detectors, each havingsignal inputs coupled to theoutput of said variable gain amplifier;

a pair of coil and magnet assemblies associated with said reticle fordeveloping periodic reference signals having phases related to theinstantaneous angular position of said reticle, said reference signalsbeing in phase quadrature with each other;

a pair of squaring circuits, each having its input in dividually coupledto the output of a different one of said coil and magnet assemblies, theoutput of each of said squaring circuits being individually coupled tothe reference input of a different one of said phase detectors;

a pair of compensation networks, each having its input coupled to theoutput of a different one of said phase detectors; and

a signal transmission circuit having its input coupled to the outputs ofsaid compensation networks and its output coupled to said missile.

12. A system for guiding a self-propelled missile having steering meanscomprising:

a source of infrared energy pulsating at a predetermined frequencydisposed on said missile and directed rearwardly thereof;

an infrared telescope having a wide field of view about an optical axis;

a reticle disposed at the focus of said infrared telescope concentricwith and transverse to the axis thereof;

means for rotating said reticle about the axis of said infraredtelescope at a predetermined speed, said reticle being transparent tosaid pulsating infrared energy and having an opaque coating arranged ina modulation pattern thereon, said coating being disposed in asinusoidally varying concentration circularly around said reticle toprovide a sinusoidal average transmissivity gradient circularly aroundsaid reticle, said coating being disposed in a varying radialconcentration increasing outwardly to provide a rapidly increasingdepth-of-modulation gradient near the center of said reticle;

a condensing lens disposed adjacent said reticle;

a large radiant energy detector disposed to receive radiant energyintercepted by said infrared telescope and passed by said reticle andsaid condensing lens;

a light pipe disposed in the center of said condensing lens to interceptradiant energy passing through the central portion of said reticle;

a small radiant energy detector disposed in said light pipe in aposition to receive radiant energy intercepted thereby;

switch means having inputs electrically coupled to said radiant energydetectors and normally passing only signals appearing at the output ofsaid large radiant energy detector, said switch means being responsiveto an applied switching signal for passing only signals appearing at theoutput of said small radiant energy detector;

a first narrowband amplifier having its input electrically coupled tosaid small radiant energy detector and having a narrow passband centeredaround said predetermined frequency;

a rectifier and filter connected to the output of said first narrowbandamplifier, said filter having a predetermined charge and discharge timeconstant;

a switch amplifier having its input electrically coupled to the outputof said rectifier and filter and having its output connected to thecontrol input of said switch means, said switch amplifier being biasedto have a predetermined input threshold level above which said switchmeans is responsive and below which said switch means is nonresponsive;

a source of voltage that exceeds said threshold a predetermined timeafter the launching of said missile electrically coupled to the input ofsaid switch amplifier;

a second narrowband amplifier having its input coupled to the output ofsaid switch means and having a narrow passband centered around saidpredetermined frequency;

an automatic gain control circuit coupled to said second narrowbandamplifier for maintaining signals at the output thereof at a constantamplitude;

an amplitude modulation demodulator having its input coupled to theoutput of said second narrowband amplifier;

a variable gain amplifier having its input coupled to the output of saiddemodulator, said variable gain amplifier having a gain that varies as afunction of an applied control voltage;

a gain control voltage source coupled to said variable gain amplifierand applying a control voltage thereto that gradually increases the gainof said variable gain amplifier from the time said missile is launched;

a pair of phase detectors, each having signal inputs coupled to theoutput of said variable gain amplifi-,

er; reference means associated with said reticle for developing a pairof periodic reference signals having phases related to the instantaneousangular position of said reticle, said reference signals being in phasequadrature with each other, each of said reference signals developed bysaid reference means being individually coupled to the reference inputofa different one of said phase detectors;

a pair of compensation networks, each having its input coupled to theoutput of a different one of said phase detectors; and

a signal transmission circuit having its input coupled to the outputs ofsaid compensation networks and its output coupled to said missile.

13. A system for guiding a self-propelled missile having steering meanscomprising:

a source of infrared energy pulsating at a substantially constantpredetermined frequency disposed on said missile and directed rearwardlythereof;

an infrared telescope having a wide field of view about an optical axis;

a reticle disposed at the focus of said infrared telescope concentricwith and transverse to the axis thereof;

means for rotating said reticle about the axis of said infraredtelescope at a substantially constant predetermined speed, said reticlebeing transparent to said pulsating infrared energy and having an opaquecoating arranged in a modulation pattern thereon, said coating beingdisposed in a sinusoidally varying concentration circularly around saidreticle to provide a sinusoidal average transmissivity gradientcircularly around said reticle, said coating being disposed in a varyingradial concentration increasing outwardly to provide a rapidlyincreasing depth-of-modulation gradient near the center of said reticle;

a condensing lens disposed adjacent said reticle;

a large radiant energy detector disposed to receive radiant energyintercepted by said infrared telescope and passed by said reticle andsaid condensing lens;

a light pipe disposed in the center of said condensing lens to interceptradiant energy passing through the central portion of said reticle;

a small radiant energy detector disposed in said light pipe in aposition to receive radiant energy intercepted thereby;

switch means having inputs electrically coupled to said radiant energydetectors and normally passing to its output only signals appearing atthe output of said large radiant energy detector, said switch meansbeing responsive to a switching signal applied at a control input forpassing only signals appearing at the output of said small radiantenergy detector;

a first narrowband amplifier having its input electrically coupled tosaid small radiant energy detector and having a narrow passband centeredaround said predetermined frequency;

a rectifier and filter connected to the output of said first narrowbandamplifier, said filter having a predetermined charge and discharge timeconstant, said switch means having its control input electricallycoupled to the output of said rectifier and filter;

a source of voltage that exceeds said threshold a predetermined timeafter the launching of said missile electrically coupled to the controlinput of said switch means;

a second narrowband amplifier having its input coupled to the output ofsaid switch means and having a narrow passband centered around saidpredetermined frequency and having an automatic gain control formaintaining signals at the output thereof at a substantially constantamplitude;

an amplitude modulation demodulator having its input coupled to theoutput of said second narrowband amplifier;

a variable gain amplifier having its input coupled to the output of saiddemodulator, said variable gain amplifier having a gain that graduallyincreases from the time said missile is launched;

a pair of phase detectors, each having signal inputs coupled to theoutput of said variable gain amplifier;

reference means associated with said reticle for developing a pair ofperiodic reference signals having phases related to the instantaneousangular position of said reticle, said reference signals being in phasequadrature with each other, each of said reference signals developed bysaid reference means being individually coupled to the reference inputof a different one of said phase detectors; and

a signal transmission circuit having its input coupled to the outputs ofsaid phase detectors and its output coupled to said missile.

14. A system for guiding a self-propelled missile having steering meanscomprising:

a source of infrared energy pulsating at a substantially constantpredetermined frequency disposed on said missile and'directed rearwardlythereof;

an infrared telescope having a wide field of view about an optical axis;

a reticle disposed at the focus of said infrared telescope concentricwith and transverse to the axis thereof;

means for rotating said reticle about the axis of said infraredtelescope at a substantially constant predetermined speed, said reticlehaving an opaque modulation pattern thereon to provide a sinusoidalaverage transmissivity gradient circularly around said reticle and toprovide a rapidly increasing depth-of-modulation gradient near thecenter of said reticle;

a condensing lens disposed adjacent said reticle;

a large radiant energy detector disposed to receive radiant energyintercepted by said infrared telescope and passed by said reticle andsaid condensing lens;

a light pipe disposed in the center of said condensing lens to interceptradiant energy passing through the central portion of said reticle;

a small radiant energy detector disposed in said light pipe in aposition to receive radiant energy intercepted thereby;

switch means having inputs electrically coupled to said radiant energydetectors and normally passing to its output only signals appearing atthe output of said large radiant energy detector, said switch meansbeing responsive to a switching signal applied at a control input forpassing only signals appearing at the output of said small radiantenergy detector;

first frequency selective means having its input electrically coupled tosaid small radiant energy detector and having a narrow frequencypassband centered around said predetermined frequency, said switch meanshaving its control input electrically coupled to the output of saidfirst frequency selective means;

a source of voltage that exceeds a predetermined value a predeterminedtime after the launching of said missile electrically coupled to thecontrol input of said switch means;

second frequency selective means having its input coupled to the outputof said switch means and having a narrow frequency passband centeredaround said predetermined frequency and having an automatic gain controlfor maintaining signals at the output thereof at a substantiallyconstant amplitude;

an amplitude modulation demodulator having its input coupled to theoutput of said second frequency selective means;

a variable gain amplifier having its input coupled to the output of saiddemodulator, said variable gain amplifier having a gain that graduallyincreases from the time said missile is launched;

phase detecting means having an input coupled to the output of saidvariable gain amplifier;

reference means associated with said reticle for developing a pair ofperiodic reference signals having phases related to the instantaneousangular position of said reticle, said reference signals being in phasequadrature with each other, said reference signals being coupled to thereference input of said phase detecting means; and

25 a signal transmission circuit having its input coupled to the outputsof said phase detecting means and its output coupled to said missile.

15. A system for guiding a self-propelled missile having steering meanscomprising:

a source of infrared energy pulsating at a predetermined frequencydisposed on said missile and directed rearwardly thereof;

an infrared telescope having a wide field of view about an optical axis;

a reticle disposed at the focus of said infrared telescope concentricwith and transverse to the axis thereof;

means for rotating said reticle about the axis of said infraredtelescope at a predetermined speed, said reticle having an opaquemodulation pattern thereon to provide a sinusoidally varying averagetransmissivity gradient circularly around said reticle and to provide arapidly increasing depth-ofmodulation gradient outward from the centerof said reticle;

a large radiant energy detector disposed to receive radiant energyintercepted by said infrared telescope and passed by said reticle;

a small radiant energy detector disposed in said infrared telescope in aposition to intercept radiant energy passing through the central portionof said reticle;

switch means having inputs electrically coupled to said radiant energydetectors and normally passing to its output only signals appearing atthe output of said large radiant energy detector, said switch meansbeing responsive to a switching signal applied at a control input forpassing only signals appearing at the output of said small radiantenergy detector;

first frequency selective means having its input electrically coupled tosaid small radiant energy detector and having a narrow frequencypassband centered around said predetermined frequency, said switch meanshaving its control input electrically coupled to the output of saidfirst frequency selective means;

second frequency selective means having its input coupled to the outputof said switch means and having a narrow frequency passband centeredaround said predetermined frequency;

an amplitude modulation demodulator having its input coupled to theoutput of said second frequency selective means;

a variable gain amplifier having its input coupled to the output of saiddemodulator and having a gain that gradually increases from the timesaid missile is launched;

phase detecting means having an input coupled to the output of saidvariable gain amplifier;

reference means associated with said reticle for developing periodicreference signals, the phase of which is related to the instantaneousangular position of said reticle, said reference signals being coupledto the reference input of said phase detecting means; and

a signal transmission circuit having its input coupled to the outputs ofsaid phase detecting means and its output coupled to said missile.

16. A system for guiding a self-propelled missile having steering meanscomprising:

a source of infrared energy pulsating at a predetermined frequencydisposed on said missile and directed rearwardly thereof;

an infrared telescope, having a wide field of view about an opticalaxis;

a reticle disposed at the focus of said infrared telescope concentricwith and transverse to the axis thereof;

means for rotating said reticle about the axis of said infraredtelescope at a predetermined speed, said reticle having an opaquemodulation pattern thereon to provide a sinusoidally varying averagetransmissivity gradient circularly around said reticle and to provide arapidly increasing depth-ofmodulation gradient outward from the centerof said reticle;

a large radiant energy detector disposed to receive radiant energyintercepted by said infrared telescope and passed by said reticle;

a small radiant energy detector disposed in said infrared telescope in aposition to intercept radiant energy passing through the central portionof said reticle;

switch means having inputs electrically coupled to said radiant energydetectors and normally passing to its output only signals appearing atthe output of said large radiant energy detector, said switch meansbeing responsive to a switching signal applied at a control input forpassing to its output only signals appearing at the output of said smallradiant energy detector;

first frequency selective means having its input electrically coupled tosaid small radiant energy detector and having a narrow frequencypassband centered around said predetermined frequency, said switch meanshaving its control input electrically coupled to the output of saidfirst frequency selective means;

second frequency selective means having its input coupled to the outputof said switch means and having a narrow frequency passband centeredaround said predetermined frequency;

an amplitude modulation demodulator having its input coupled to theoutput of said second frequency selective means;

phase detecting means having an input coupled to the output of saiddemodulator;

reference means associated with said reticle for developing periodicreference signals, the phase of which is related to the instantaneousangular position of said reticle, said reference signals being coupledto the reference input of said phase detecting means; and

a signal transmission circuit having its input coupled to the outputs ofsaid phase detecting means and its output coupled to said missile.

17. An interrupted radiation source comprising:

a radiating member having a radiating surface;

means adjacent said member for heating said radiating surface;

driving means disposed adjacent said radiating member and having a shaftspaced away from and generally parallel to said radiating surface; and

a plane interruption member of substantially the same size and shape assaid radiating member and mechanically coupled at its edge to the shaftof said driving means for rotation thereby about an axis parallel withthe plane surfaces of said interruption member, said interruption memberbeing disposed to shield said radiating member twice during eachrevolution about said axis.

18. An interrupted radiation source comprising:

a cylindrical housing sealed at one end by a heat-resistant disk;

a pyrotechnic composition disposed inside said housing;

an electrically operated firing squib disposed inside said housing incontact with said pyrotechnic composition;

at least one piece of iron within said housing and embedded in saidpyrotechnic composition;

a speed-regulated motor secured to the outside of said housing andhaving its shaft spaced away from and parallel to the plane outersurface of said heatresistant disk; and

an interruption disk of substantially the same size as saidheat-resistant disk and mechanically coupled at its circumference to theshaft of said motor for rotation thereby about an axis parallel with theplane surfaces of said interruption disk, said interruption disk beingdisposed to shield said heat-resistant disk twice during each revolutionabout said axis.

19. An interrupted radiation source comprising:

a cylindrical housing sealed at one end by a molybdenum disk having azirconium carbide coating;

a pyrotechnic composition disposed inside said housing and composed of56 percent iron oxide, 14 percent aluminum powder, 3 percent boron and27 percent barium chromate;

an electrically operated firing squib disposed inside said housing incontact with said pyrotechnic composition;

at least one piece of iron within said housing and embedded in saidpyrotechnic composition;

a speed-regulated motor secured to the outside of said housing andhaving its shaft spaced away from and parallel to the plane outersurface of said molybdenum disk; and an interruption disk ofsubstantially the same size as said molybdenum disk and mechanicallycoupled zone, said first and second zones being 180 opposed.

tric fields of view comprising:

a cylindrical outer case having an entrance window at one end thereof;

at its circumference to the shaft of id m tor f first and secondobjective lenses having a wide field rotation thereby ab t a xi ll l ithth of view and disposed within said case adjacent said plane surfaces ofsaid interruption disk, said inter- Wmdow; ruption di k b i disposed toShield Said mo|yb a transparent image surface disposed within said casedenum disk twice during each revolution about at the focus ofsaldoblectlvekfnsl d axis a condensing lens disposed within said caseadjacent 20. A reticle for amplitude modulating radiant enersald Imagesurface; gy Comprising; a large radiant energy detector disposed withinsaid a disk transparent to said radiant energy; case at a location toreceive radiant energy a coating opaque to said radiant energy disposedon focused lmag? surface and Passed by Sam said disk in a pattern, saidpattern comprising conlens centric circular opaque lines having aprogressivea hght dlsposed m h center of Sa1d cndensmg ly varying widtharound said disk, increasing from lens to mtercePt .energy passingthrough a minimum at a first radial zone on said disk to a the centrii]porno Ofsald Image: Surface i q maximum at a second radial zone on saiddisk and 3 i i i i y detector.dlspos.ed wlthm szild decreasing to Saidminimum at said first radial light pipe in a position to receive radiantenergy intercepted thereby. 23. In an infrared tracker, apparatus fordeveloping a signal indicative of the instantaneous angular-position ofamodulating reticle said apparatus comprising: a cylmdrlca reticle holderof nonmagnetic material 21. A reticle for amplitude modulating radiantenergy comprising:

a disk transparent to said radiant energy;

a coating opaque to said radiant energy disposed on said disk in apattern, said pattern comprising concentric circular opaque lines havinga progressively varying width around said disk, increasing fromrotatably disposed in said infrared tracker and containing saidmodulating reticle;

driving means mechanically coupled to said reticle holder for rotationthereof;

a band of magnetic material fixed to the outside of a minimum at a firstradial zone on said disk to a said reticle holder, said band varyinglinearly in maximum at a second radial zone on said disk and width froma maximum width to a minimum width; decreasing to said minimu at id fi tdi l a pair of magnetic pole pieces, each disposed with an one, saidfirst and second zones being 180 OP- edge adjacent said band, the Widthof the adjacent posed, said concentric circular opaque lines havedges ofSaid P Pieces being Substantially equal ing a progressively increasingmaximum width from the center of said disk to the circumference thereof,the spacing between adjacent ones of said concentric circular opaquelines in said second zone progressively decreasing from the center ofsaid disk to the circumference thereof.

to the maximum width of said band;

a permanent magnet having each of its poles individually magneticallycoupled to a different one of said pole pieces; and

a coil of wire wound around said permanent magnet.

1. An automatic missile guidance system for guiding a missile along aline-of-sight to a target established by a human operator, said missilehaving guidance means comprising: a guidance unit for developingsteering signals related to the deviation of said missile from saidline-of-sight; means for transmitting said guidance signals from saidguidance unit to said missile; and a source of pulsating radiant energyon said missile and directed to the rear thereof, said source of radiantenergy having a predetermined pulsation frequency, said guidance unitbeing selectively responsive to said radiant energy at saidpredetermined pulsation frequency.
 2. The automatic missile guidancesystem of claim 1 wherein said guidance unit has means for narrowing itsfield of view when said missile is proximate to said line-of-sight. 3.The automatic missile guidance system of claim 2 wherein said guidanceunit has a radiant energy receiver thereon adapted to receive radiantenergy from said source of pulsating radiant energy on said missile,said radiant energy receiving means having a large radiant energydetector disposed therein to receive radiant energy in any part of thefield of view and a small radiant energy detector disposed therein, saidsmall radiant energy detector being positioned to receive radiant energyin the central portion of the field of view of said radiant energyreceiver, and switch means for switching between said large and saidsmall radiant energy detectors in response to position of missile sourceimage in field of view.
 4. The automatic missile guidance system ofclaim 3 wherein said small radiant energy detector means has an outputto said switch means to switch said switch means so that its smallradiant energy detector means is switched to control said missile whenthe input radiance to said small radiant energy detection means exceedsa predetermined value.
 5. The automatic missile guidance system of claim4 wherein said source of pulsating radiant energy on said missileoperates at a substantially constant frequency.
 6. The automatic missileguidance system of claim 5 wherein said radiant energy receiving meanson said guidance unit comprises a telescope having a wide field of viewabout an optical axis, a reticle disposed at the focus of said telescopeconcentric with and transverse to the axis thereof, means rotating saidreticle about the axis of said telescope at a predetermined speed, saidreticle having an opaque modulation pattern thereon to provide asubstantially sinusoidally varying average transmissivity gradientcircularly around said reticle and to provide a rapidly increasingdepth-of-modulation gradient outward from the center of said reticle,said large radiant energy detector being disposed to receive radiantenergy passed by said reticle, said small radiant energy detector beingdisposed in a position to intercept radiant energy passing through thecentral portion of said reticle.
 7. The automatic missile guidancesystem of claim 3 wherein the output of said switch is connected tofirst and second phase detectors, for respectively detecting pitch andyaw of said missile, said phase detectors being connected to saidmissile to guide said missile.
 8. The automatic missile guidance systemof claim 7 wherein said means for transmitting said guidance signalsfrom said guidance unit to said missile comprises at least one wireinterconnected bEtween said guidance unit and said missile.
 9. Anautomatic missile guidance system for guiding a missile along aline-of-sight to a target established by a human operator, said missilehaving guidance means comprising: a guidance unit for developingsteering signals related to the deviation of said missile from saidline-of-sight; means for transmitting said guidance signals from saidguidance unit to said missile; and a source of pulsating radiant energyon said missile and directed to the rear thereof, said source of radiantenergy having a predetermined substantially constant pulsationfrequency, said guidance unit being selectively responsive to saidradiant energy at said predetermined substantially constant pulsationfrequency, said guidance unit having means for narrowing its field ofview when said missile is proximate to said line-of-sight.
 10. A systemfor guiding a self-propelled missile having steering means comprising:means disposed on said missile for emitting radiant energy pulsating ata predetermined frequency rearwardly thereof; means for interceptingradiant energy having a wide field of view; means disposed within saidinterception means for amplitude modulating intercepted radiant energyat a predetermined frequency; a large radiant energy detector disposedto receive radiant energy intercepted by said interception means andmodulated by said modulation means; a small radiant energy detectordisposed within said interception means in a position to receive radiantenergy in the central portion of the field of view of said interceptionmeans and modulated by said modulation means; switch means having inputselectrically coupled to said radiant energy detectors and normallypassing to its output only signals appearing at the output of said largeradiant energy detector, said switch means being responsive to aswitching signal applied at a control input for passing to its outputonly signals appearing at the output of said small radiant energydetector; first frequency selective means having its input electricallycoupled to said small radiant energy detector and having a narrowfrequency passband centered around said predetermined frequency, saidswitch means having its control input electrically coupled to the outputof said first frequency selective means; second frequency selectivemeans having its input coupled to the output of said switch means andhaving a narrow frequency passband centered around said predeterminedfrequency; an amplitude modulation demodulator having its input coupledto the output of said second frequency selective means; phase detectingmeans having an input coupled to the output of said demodulator;reference means associated with said modulation means for developingperiodic reference signals, the phase of which is related to the phaseof said modulation means, said reference signals being coupled to thereference input of said phase detecting means; and signal transmissionmeans having its input coupled to the outputs of said phase detectingmeans and its output coupled to said missile.
 11. A guided missilesystem comprising: a self-propelled missile having steering means; asource of infrared energy pulsating at a substantially constantpredetermined frequency disposed on said missile and directed rearwardlythereof; a visual telescope having an optical axis; an infraredtelescope having an optical axis substantially aligned with the opticalaxis of said visual telescope and having a wide field of view; a reticledisposed at the focus of said infrared telescope concentric with andtransverse to the axis thereof; means for rotating said reticle aboutthe axis of said infrared telescope at a predetermined speed, saidreticle being transparent to said pulsating infrared energy and havingan opaque coating arranged in a modulation pattern thereon, said coatingbeing disposed in a sinusoidally varying concentration ciRcularly aroundsaid reticle to provide a sinusoidal average transmissivity gradientcircularly around said reticle, said coating being disposed in a varyingradial concentration increasing outwardly to provide a rapidlyincreasing depth-of-modulation gradient near the center of said reticle;a condensing lens disposed adjacent said reticle; a large radiant energydetector disposed to receive radiant energy intercepted by said infraredtelescope and passed by said reticle and said condensing lens; a lightpipe disposed in the center of said condensing lens to intercept radiantenergy passing through the central portion of said reticle; a smallradiant energy detector disposed in said light pipe in a position toreceive radiant energy intercepted thereby; an electromagnetic relayhaving a normally open contact; a normally closed contact; a switch armand an actuating coil, said small radiant energy detector beingelectrically coupled to the normally open contact of said relay, saidlarge radiant energy detector being electrically coupled to the normallyclosed contact of said relay; a first narrowband amplifier having itsinput electrically coupled to said small radiant energy detector andhaving a narrow passband centered around said predetermined frequency; arectifier and filter connected to the output of said first narrowbandamplifier, said filter having a predetermined charge and discharge timeconstant; a switch amplifier having its input electrically coupled tothe output of said rectifier and filter and having its output connectedto the actuating coil of said relay, said switch amplifier being biasedto have a predetermined input threshold level above which said relay isenergized and below which said relay is de-energized; a source ofvoltage that exceeds said threshold a predetermined time after thelaunching of said missile electrically coupled to the input of saidswitch amplifier; a second narrowband amplifier having its input coupledto the switch arm of said relay and having a narrow passband centeredaround said predetermined frequency; an automatic gain control circuitcoupled to said second narrowband amplifier for maintaining signals atthe output thereof at a constant amplitude; an amplitude modulationdemodulator having its input coupled to the output of said secondnarrowband amplifier; a variable gain amplifier having its input coupledto the output of said demodulator, said variable gain amplifier having again that varies as a function of an applied control voltage; a gaincontrol voltage source coupled to said variable gain amplifier andapplying a control voltage thereto that gradually increases the gain ofsaid variable gain amplifier from the time said missile is launched; apair of phase detectors, each having signal inputs coupled to the outputof said variable gain amplifier; a pair of coil and magnet assembliesassociated with said reticle for developing periodic reference signalshaving phases related to the instantaneous angular position of saidreticle, said reference signals being in phase quadrature with eachother; a pair of squaring circuits, each having its input individuallycoupled to the output of a different one of said coil and magnetassemblies, the output of each of said squaring circuits beingindividually coupled to the reference input of a different one of saidphase detectors; a pair of compensation networks, each having its inputcoupled to the output of a different one of said phase detectors; and asignal transmission circuit having its input coupled to the outputs ofsaid compensation networks and its output coupled to said missile.
 12. Asystem for guiding a self-propelled missile having steering meanscomprising: a source of infrared energy pulsating at a predeterminedfrequency disposed on said missile and directed rearwardly thereof; aninfrared telescope having a wide field of view about an Optical axis; areticle disposed at the focus of said infrared telescope concentric withand transverse to the axis thereof; means for rotating said reticleabout the axis of said infrared telescope at a predetermined speed, saidreticle being transparent to said pulsating infrared energy and havingan opaque coating arranged in a modulation pattern thereon, said coatingbeing disposed in a sinusoidally varying concentration circularly aroundsaid reticle to provide a sinusoidal average transmissivity gradientcircularly around said reticle, said coating being disposed in a varyingradial concentration increasing outwardly to provide a rapidlyincreasing depth-of-modulation gradient near the center of said reticle;a condensing lens disposed adjacent said reticle; a large radiant energydetector disposed to receive radiant energy intercepted by said infraredtelescope and passed by said reticle and said condensing lens; a lightpipe disposed in the center of said condensing lens to intercept radiantenergy passing through the central portion of said reticle; a smallradiant energy detector disposed in said light pipe in a position toreceive radiant energy intercepted thereby; switch means having inputselectrically coupled to said radiant energy detectors and normallypassing only signals appearing at the output of said large radiantenergy detector, said switch means being responsive to an appliedswitching signal for passing only signals appearing at the output ofsaid small radiant energy detector; a first narrowband amplifier havingits input electrically coupled to said small radiant energy detector andhaving a narrow passband centered around said predetermined frequency; arectifier and filter connected to the output of said first narrowbandamplifier, said filter having a predetermined charge and discharge timeconstant; a switch amplifier having its input electrically coupled tothe output of said rectifier and filter and having its output connectedto the control input of said switch means, said switch amplifier beingbiased to have a predetermined input threshold level above which saidswitch means is responsive and below which said switch means isnonresponsive; a source of voltage that exceeds said threshold apredetermined time after the launching of said missile electricallycoupled to the input of said switch amplifier; a second narrowbandamplifier having its input coupled to the output of said switch meansand having a narrow passband centered around said predeterminedfrequency; an automatic gain control circuit coupled to said secondnarrowband amplifier for maintaining signals at the output thereof at aconstant amplitude; an amplitude modulation demodulator having its inputcoupled to the output of said second narrowband amplifier; a variablegain amplifier having its input coupled to the output of saiddemodulator, said variable gain amplifier having a gain that varies as afunction of an applied control voltage; a gain control voltage sourcecoupled to said variable gain amplifier and applying a control voltagethereto that gradually increases the gain of said variable gainamplifier from the time said missile is launched; a pair of phasedetectors, each having signal inputs coupled to the output of saidvariable gain amplifier; reference means associated with said reticlefor developing a pair of periodic reference signals having phasesrelated to the instantaneous angular position of said reticle, saidreference signals being in phase quadrature with each other, each ofsaid reference signals developed by said reference means beingindividually coupled to the reference input of a different one of saidphase detectors; a pair of compensation networks, each having its inputcoupled to the output of a different one of said phase detectors; and asignal transmission circuit having its input coupled to the outputs ofsaid compensation networks and its output couPled to said missile.
 13. Asystem for guiding a self-propelled missile having steering meanscomprising: a source of infrared energy pulsating at a substantiallyconstant predetermined frequency disposed on said missile and directedrearwardly thereof; an infrared telescope having a wide field of viewabout an optical axis; a reticle disposed at the focus of said infraredtelescope concentric with and transverse to the axis thereof; means forrotating said reticle about the axis of said infrared telescope at asubstantially constant predetermined speed, said reticle beingtransparent to said pulsating infrared energy and having an opaquecoating arranged in a modulation pattern thereon, said coating beingdisposed in a sinusoidally varying concentration circularly around saidreticle to provide a sinusoidal average transmissivity gradientcircularly around said reticle, said coating being disposed in a varyingradial concentration increasing outwardly to provide a rapidlyincreasing depth-of-modulation gradient near the center of said reticle;a condensing lens disposed adjacent said reticle; a large radiant energydetector disposed to receive radiant energy intercepted by said infraredtelescope and passed by said reticle and said condensing lens; a lightpipe disposed in the center of said condensing lens to intercept radiantenergy passing through the central portion of said reticle; a smallradiant energy detector disposed in said light pipe in a position toreceive radiant energy intercepted thereby; switch means having inputselectrically coupled to said radiant energy detectors and normallypassing to its output only signals appearing at the output of said largeradiant energy detector, said switch means being responsive to aswitching signal applied at a control input for passing only signalsappearing at the output of said small radiant energy detector; a firstnarrowband amplifier having its input electrically coupled to said smallradiant energy detector and having a narrow passband centered aroundsaid predetermined frequency; a rectifier and filter connected to theoutput of said first narrowband amplifier, said filter having apredetermined charge and discharge time constant, said switch meanshaving its control input electrically coupled to the output of saidrectifier and filter; a source of voltage that exceeds said threshold apredetermined time after the launching of said missile electricallycoupled to the control input of said switch means; a second narrowbandamplifier having its input coupled to the output of said switch meansand having a narrow passband centered around said predeterminedfrequency and having an automatic gain control for maintaining signalsat the output thereof at a substantially constant amplitude; anamplitude modulation demodulator having its input coupled to the outputof said second narrowband amplifier; a variable gain amplifier havingits input coupled to the output of said demodulator, said variable gainamplifier having a gain that gradually increases from the time saidmissile is launched; a pair of phase detectors, each having signalinputs coupled to the output of said variable gain amplifier; referencemeans associated with said reticle for developing a pair of periodicreference signals having phases related to the instantaneous angularposition of said reticle, said reference signals being in phasequadrature with each other, each of said reference signals developed bysaid reference means being individually coupled to the reference inputof a different one of said phase detectors; and a signal transmissioncircuit having its input coupled to the outputs of said phase detectorsand its output coupled to said missile.
 14. A system for guiding aself-propelled missile having steering means comprising: a source ofinfrared energy pulsating at a substantially constant predeterminedfrequency disposed on said missilE and directed rearwardly thereof; aninfrared telescope having a wide field of view about an optical axis; areticle disposed at the focus of said infrared telescope concentric withand transverse to the axis thereof; means for rotating said reticleabout the axis of said infrared telescope at a substantially constantpredetermined speed, said reticle having an opaque modulation patternthereon to provide a sinusoidal average transmissivity gradientcircularly around said reticle and to provide a rapidly increasingdepth-of-modulation gradient near the center of said reticle; acondensing lens disposed adjacent said reticle; a large radiant energydetector disposed to receive radiant energy intercepted by said infraredtelescope and passed by said reticle and said condensing lens; a lightpipe disposed in the center of said condensing lens to intercept radiantenergy passing through the central portion of said reticle; a smallradiant energy detector disposed in said light pipe in a position toreceive radiant energy intercepted thereby; switch means having inputselectrically coupled to said radiant energy detectors and normallypassing to its output only signals appearing at the output of said largeradiant energy detector, said switch means being responsive to aswitching signal applied at a control input for passing only signalsappearing at the output of said small radiant energy detector; firstfrequency selective means having its input electrically coupled to saidsmall radiant energy detector and having a narrow frequency passbandcentered around said predetermined frequency, said switch means havingits control input electrically coupled to the output of said firstfrequency selective means; a source of voltage that exceeds apredetermined value a predetermined time after the launching of saidmissile electrically coupled to the control input of said switch means;second frequency selective means having its input coupled to the outputof said switch means and having a narrow frequency passband centeredaround said predetermined frequency and having an automatic gain controlfor maintaining signals at the output thereof at a substantiallyconstant amplitude; an amplitude modulation demodulator having its inputcoupled to the output of said second frequency selective means; avariable gain amplifier having its input coupled to the output of saiddemodulator, said variable gain amplifier having a gain that graduallyincreases from the time said missile is launched; phase detecting meanshaving an input coupled to the output of said variable gain amplifier;reference means associated with said reticle for developing a pair ofperiodic reference signals having phases related to the instantaneousangular position of said reticle, said reference signals being in phasequadrature with each other, said reference signals being coupled to thereference input of said phase detecting means; and a signal transmissioncircuit having its input coupled to the outputs of said phase detectingmeans and its output coupled to said missile.
 15. A system for guiding aself-propelled missile having steering means comprising: a source ofinfrared energy pulsating at a predetermined frequency disposed on saidmissile and directed rearwardly thereof; an infrared telescope having awide field of view about an optical axis; a reticle disposed at thefocus of said infrared telescope concentric with and transverse to theaxis thereof; means for rotating said reticle about the axis of saidinfrared telescope at a predetermined speed, said reticle having anopaque modulation pattern thereon to provide a sinusoidally varyingaverage transmissivity gradient circularly around said reticle and toprovide a rapidly increasing depth-of-modulation gradient outward fromthe center of said reticle; a large radiant energy detector disposed toreceive radiant energy intercepted by said infrared telescoPe and passedby said reticle; a small radiant energy detector disposed in saidinfrared telescope in a position to intercept radiant energy passingthrough the central portion of said reticle; switch means having inputselectrically coupled to said radiant energy detectors and normallypassing to its output only signals appearing at the output of said largeradiant energy detector, said switch means being responsive to aswitching signal applied at a control input for passing only signalsappearing at the output of said small radiant energy detector; firstfrequency selective means having its input electrically coupled to saidsmall radiant energy detector and having a narrow frequency passbandcentered around said predetermined frequency, said switch means havingits control input electrically coupled to the output of said firstfrequency selective means; second frequency selective means having itsinput coupled to the output of said switch means and having a narrowfrequency passband centered around said predetermined frequency; anamplitude modulation demodulator having its input coupled to the outputof said second frequency selective means; a variable gain amplifierhaving its input coupled to the output of said demodulator and having again that gradually increases from the time said missile is launched;phase detecting means having an input coupled to the output of saidvariable gain amplifier; reference means associated with said reticlefor developing periodic reference signals, the phase of which is relatedto the instantaneous angular position of said reticle, said referencesignals being coupled to the reference input of said phase detectingmeans; and a signal transmission circuit having its input coupled to theoutputs of said phase detecting means and its output coupled to saidmissile.
 16. A system for guiding a self-propelled missile havingsteering means comprising: a source of infrared energy pulsating at apredetermined frequency disposed on said missile and directed rearwardlythereof; an infrared telescope, having a wide field of view about anoptical axis; a reticle disposed at the focus of said infrared telescopeconcentric with and transverse to the axis thereof; means for rotatingsaid reticle about the axis of said infrared telescope at apredetermined speed, said reticle having an opaque modulation patternthereon to provide a sinusoidally varying average transmissivitygradient circularly around said reticle and to provide a rapidlyincreasing depth-of-modulation gradient outward from the center of saidreticle; a large radiant energy detector disposed to receive radiantenergy intercepted by said infrared telescope and passed by saidreticle; a small radiant energy detector disposed in said infraredtelescope in a position to intercept radiant energy passing through thecentral portion of said reticle; switch means having inputs electricallycoupled to said radiant energy detectors and normally passing to itsoutput only signals appearing at the output of said large radiant energydetector, said switch means being responsive to a switching signalapplied at a control input for passing to its output only signalsappearing at the output of said small radiant energy detector; firstfrequency selective means having its input electrically coupled to saidsmall radiant energy detector and having a narrow frequency passbandcentered around said predetermined frequency, said switch means havingits control input electrically coupled to the output of said firstfrequency selective means; second frequency selective means having itsinput coupled to the output of said switch means and having a narrowfrequency passband centered around said predetermined frequency; anamplitude modulation demodulator having its input coupled to the outputof said second frequency selective means; phase detecting means havingan input coupled to the output of said demodulaTor; reference meansassociated with said reticle for developing periodic reference signals,the phase of which is related to the instantaneous angular position ofsaid reticle, said reference signals being coupled to the referenceinput of said phase detecting means; and a signal transmission circuithaving its input coupled to the outputs of said phase detecting meansand its output coupled to said missile.
 17. An interrupted radiationsource comprising: a radiating member having a radiating surface; meansadjacent said member for heating said radiating surface; driving meansdisposed adjacent said radiating member and having a shaft spaced awayfrom and generally parallel to said radiating surface; and a planeinterruption member of substantially the same size and shape as saidradiating member and mechanically coupled at its edge to the shaft ofsaid driving means for rotation thereby about an axis parallel with theplane surfaces of said interruption member, said interruption memberbeing disposed to shield said radiating member twice during eachrevolution about said axis.
 18. An interrupted radiation sourcecomprising: a cylindrical housing sealed at one end by a heat-resistantdisk; a pyrotechnic composition disposed inside said housing; anelectrically operated firing squib disposed inside said housing incontact with said pyrotechnic composition; at least one piece of ironwithin said housing and embedded in said pyrotechnic composition; aspeed-regulated motor secured to the outside of said housing and havingits shaft spaced away from and parallel to the plane outer surface ofsaid heat-resistant disk; and an interruption disk of substantially thesame size as said heat-resistant disk and mechanically coupled at itscircumference to the shaft of said motor for rotation thereby about anaxis parallel with the plane surfaces of said interruption disk, saidinterruption disk being disposed to shield said heat-resistant disktwice during each revolution about said axis.
 19. An interruptedradiation source comprising: a cylindrical housing sealed at one end bya molybdenum disk having a zirconium carbide coating; a pyrotechniccomposition disposed inside said housing and composed of 56 percent ironoxide, 14 percent aluminum powder, 3 percent boron and 27 percent bariumchromate; an electrically operated firing squib disposed inside saidhousing in contact with said pyrotechnic composition; at least one pieceof iron within said housing and embedded in said pyrotechniccomposition; a speed-regulated motor secured to the outside of saidhousing and having its shaft spaced away from and parallel to the planeouter surface of said molybdenum disk; and an interruption disk ofsubstantially the same size as said molybdenum disk and mechanicallycoupled at its circumference to the shaft of said motor for rotationthereby about an axis parallel with the plane surfaces of saidinterruption disk, said interruption disk being disposed to shield saidmolybdenum disk twice during each revolution about said axis.
 20. Areticle for amplitude modulating radiant energy comprising: a disktransparent to said radiant energy; a coating opaque to said radiantenergy disposed on said disk in a pattern, said pattern comprisingconcentric circular opaque lines having a progressively varying widtharound said disk, increasing from a minimum at a first radial zone onsaid disk to a maximum at a second radial zone on said disk anddecreasing to said minimum at said first radial zone, said first andsecond zones being 180* opposed.
 21. A reticle for amplitude modulatingradiant energy comprising: a disk transparent to said radiant energy; acoating opaque to said radiant energy disposed on said disk in apattern, said pattern comprising concentric circular opaque lines havinga progressively varying width around said disk, increasIng from aminimum at a first radial zone on said disk to a maximum at a secondradial zone on said disk and decreasing to said minimum at said firstradial zone, said first and second zones being 180* opposed, saidconcentric circular opaque lines having a progressively increasingmaximum width from the center of said disk to the circumference thereof,the spacing between adjacent ones of said concentric circular opaquelines in said second zone progressively decreasing from the center ofsaid disk to the circumference thereof.
 22. A radiant energy telescopehaving dual, concentric fields of view comprising: a cylindrical outercase having an entrance window at one end thereof; first and secondobjective lenses having a wide field of view and disposed within saidcase adjacent said window; a transparent image surface disposed withinsaid case at the focus of said objective lens; a condensing lensdisposed within said case adjacent said image surface; a large radiantenergy detector disposed within said case at a location to receiveradiant energy focused on said image surface and passed by saidcondensing lens; a light pipe disposed in the center of said condensinglens to intercept radiant energy passing through the central portion ofsaid image surface; and a small radiant energy detector disposed withinsaid light pipe in a position to receive radiant energy interceptedthereby.
 23. In an infrared tracker, apparatus for developing a signalindicative of the instantaneous angular position of a modulatingreticle, said apparatus comprising: a cylindrical reticle holder ofnonmagnetic material rotatably disposed in said infrared tracker andcontaining said modulating reticle; driving means mechanically coupledto said reticle holder for rotation thereof; a band of magnetic materialfixed to the outside of said reticle holder, said band varying linearlyin width from a maximum width to a minimum width; a pair of magneticpole pieces, each disposed with an edge adjacent said band, the width ofthe adjacent edges of said pole pieces being substantially equal to themaximum width of said band; a permanent magnet having each of its polesindividually magnetically coupled to a different one of said polepieces; and a coil of wire wound around said permanent magnet.